Adenosine is a purine which contributes to intermediary metabolism and participates in the regulation of physiological activity in a variety of mammalian tissues. Adenosine participates in many local regulatory mechanisms, in particular synapses in the central nervous system (CNS) and at neuroeffector junctions in the peripheral nervous system. In the CNS, adenosine: inhibits the release of a variety of neurotransmitters, such as acetylcholine, noradrenaline, dopemine, serotonin, glutamate, and GABA; depresses neurotransmission; reduces neuronal firing to induce spinal analgesia; and possesses anxiolytic properties. See A. Pelleg and R. Porter, Pharmacotherapy 10(2), 157 (1990); J. Daval, et el., Life Sciences 49:1435 (1991). In the heart, adenosine suppresses pacemaker activity, slows AV conduction, possesses antiarrhythmic and arrhythmogenic effects, modulates autonomic control, and triggers the synthesis and release of prostaglandins. See K. Mullane and M. William, Adenosine and Adenosine Receptors p. 289 (M. Williams, ed. Humana Press, 1990). Adenosine has potent vasodilatory effects and modulates vascular tone. See A Deuseen et al., J. Pflugers Arch. 406:608 (1986). Adenosine is currently being used clinically for the treatment of superventricular tachycardia and other cardiac anomalies. See C. Chronister, American Journal of Critical Care 2(1): 41-47 (1993). Adenosine analogues are being investigated for use as anticonvulsant, anxiolytic and neuroprotective agents. See M. Higgins et al., Pharmacy World & Science 16(2): 62-68 (1994).
Adenosine has also been implicated as a primary determinant underlying the symptoms of bronchial asthma. It induces bronchoconstriction and the contraction of airway smooth muscle. See J. Thorne and K. Broadley, American Journal of Respiratory & Critical Care Medicine 149(2 pt. 1): 392-399 (1994); S. Ali et al., Agents & Actions 37(3-4): 165-167 (1992). Adenosine causes bronchoconstriction in asthmatics but not in non-asthmatics. See Bjorck et al., American Review of Respiratory Disease 145(5): 1087-1091 (1992); S. Holgate et al., Annals of the New York Academy of Sciences 629: 227-236 (1991).
In view of the foregoing, it will be readily apparent that: (i) adenosine depletion can lead to a broad variety of deleterious conditions, and that methods of treating adenosine depletion can be an extremely useful means of therapeutic intervention; and (ii) methods of inducing adenosine depletion can also be useful in treating conditions such as asthma.